Cavity-sinking or wire-EDM is now already state of the art with excellent surface quality of R.sub.a &lt;0.1 .mu.m and at a material defect of the surface with a depth of less than 1 .mu.m. Such machining requires generators that can generate monopolar or bipolar pulses in the megahertz range with current intensities around 1A This type of generator for ac pulses is disclosed in DE 40 11 752 A1. An oscillating resonance circuit at resonance gap widths to 20 pm and alternating current frequencies to 30 MHz is proposed with the purpose of permitting novel resonance machining during wire-EDM. However, an interfering self-control effect of the wire electrode has to be involved, which can cause errors in contour trueness on the order of the resonance gap width (20 .mu.m). This effect is known to anyone skilled in EDM, who has already worked with finishing pulses at frequencies above 100 kHz. It is established that, despite trouble-free servocontrol and compensation of the contouring errors of the wire electrode, sharp external contours are rounded and inside corners have material excess. The more often such a fine cut is repeated, the poorer the precision. It is also found that the vertical profile becomes increasingly bulged, convexly bulged in the zones with material excess and concavely bulged in the zones with too much material removal.
It is also known that the electrical resistance of the spark gap in EDM during additionally generated periodic pauses can be determined by means of a measurement current source and the servodrive, rinsing device and generator controlled with it (CH 650 433). This process has the task of determining the degree of contamination, as well as the discharge concentration during cavity-sinkig EDM from the electrical resistance and controlling the process with reference to this value so that higher cutting performance is achieved during unsupervised operation.
In the interest of suppressing wire vibrations that can occur during EDM, it is known that such vibrations can be detected (JP 09248717 A, JP 63-216631, JP 63-22922). Lastly, Japanese Pat. Appi. No. 63-312020 discloses an EDM device wherein the vibration of the working electrode in the direction of machining a workpiece is detected. A machining gain is set in accordance with the amplitude of the vibration of the working electrode. The EDM operation can therefore be constantly performed with optimum machining gain in accordance with the change and fluctuation of the machining conditions.